Presbyopia, the age related loss of accommodation, affects everyone by about age 50. The impact of presbyopia on society is considerable from an economic and a quality of life standpoint. Although presbyopia is classically attributed to sclerosis of the lens, the precise causes remain unclear. Studies on humans and monkeys show age changes in both the crystalline lens and the extralenticular accommodative apparatus. No widely accepted cures or preventions for presbyopia currently exist, although the possibility of restoring accommodation using surgical procedures or intraocular accommodative lenses is under investigation. This application proposes 1) using central stimulation of the Edinger-Westphal (EW) nucleus of the brain in rhesus monkeys together with dynamic analyses to better understand how the young monkey eye undergoes accommodative optical changes, 2) to use in vitro mechanical stretching of monkey lenses to study the accommodative optical changes and to understand if these are similar to those that occur in vivo with natural accommodation and 3) to determine if and how the dynamic and accommodative optical performance of the monkey eye changes with age as rhesus monkeys develop presbyopia. Two experimental approaches will be used; 1) accommodative optical and geometric changes in the lens will be measured dynamically during EW stimulated accommodation in anesthetized monkeys. The dynamic accommodative responses will be compared in "young" and "middle-aged" monkeys. 2) In vitro mechanical stretching experiments will be performed on partially dissected enucleated monkey eyes to artificially induce accommodative changes in the lens. The mechanically induced optical and geometric changes will be compared with those that occur during accommodation in vivo and as a function of age. The results will quantify the dynamic accommodative responses in monkey eyes to understand the dynamics of accommodation, will allow a determination of the differences and similarities in the accommodative changes between in vitro mechanical stretching and in vivo accommodation of the lens and on how the accommodative performance of the monkey lens changes with age. The goal of this research is to gain a better understanding of how the monkey lens undergoes physical and optical accommodative changes and contribute to the progression of presbyopia. This research will provide a foundation for studies directed at understanding if accommodation can be restored with artificial accommodative intraocular lenses.